It is known to start an internal combustion engine without the use of a starter by injecting fuel into a cylinder, the piston of which is in a power phase, and by igniting the injected fuel.
The igniting of an internal combustion engine without the use of a starter is necessary in particular to set an engine, which is being operated with many stop phases, running again without high electrical energy. For example, in the case of fuel-economy engines, the engines are stopped during stop phases, for example at traffic lights or upon other interruptions to travel, and the internal combustion engine is restarted by actuation, for example of the clutch.
From DE 199 55 857 A1 and from DE 100 20 325 A1 corresponding methods of starting an internal combustion engine are known. Here an internal combustion engine, in particular for a motor vehicle, is described, which is provided with pistons that are movable [in] a cylinder and act upon a crankshaft. During operation of the internal combustion engine the piston runs through an induction phase, a compression phase, a power phase and an exhaust phase. A controller is further provided, by means of which fuel is injected in a first operating mode during a compression phase or in a second operating mode during an induction phase directly into a combustion chamber delimited by the cylinder and the piston. The controller is designed in such a way that in order to start the internal combustion engine in the stationary state of the crankshaft fuel is injected into the cylinder, the piston of which is in the compression phase, and ignited so that the crankshaft moves backwards. In this case, it may be disadvantageous that a cylinder can no longer be used for compression and ignition because combustion residues of a not yet exhausted combustion pre-gas are present, with the result that a combustible mixture does not exist.
It could moreover be disadvantageous if the engine is stationary for an extended period because then the pressure in the compression cylinder has dropped to such an extent that reliable ignition cannot occur. As with direct starting, the starting capability depends upon the filling volume, the state of the piston and also upon the length of time between stop and start. The pressure in the cylinder to be ignited lasts for a short time only. After a longer pause between stop and start the pressure adjusts itself to the ambient pressure. The residual volume may then have a lower oxygen content. A further drawback is that parasitic residual gases further impair the ignitability.